(1) Field of the Invention
The present invention relates to a process for producing a perforated ceramic. More particularly, the present invention relates to a process for producing a perforated ceramic, which process can form perforations of desired diameter at desired portions in a ceramic shaped material, without employing machining.
(2) Description of the Prior Art
Ceramic materials such as silicon nitride, silicon carbide, partially stabilized zirconia and the like have excellent properties such as high heat resistance, high abrasion resistance, high hardness, high corrosion resistance and the like, and accordingly are in wide use as mechanical parts. These ceramic materials are finding applications in increasing fields owing to continual improvements, design optimization, etc.
For such ceramic materials, perforations of desired diameter at desired portions are desirable under certain circumstances. For example, in a ceramic turbine blade 1 as shown in FIGS. 4(a) and 4(b), in order to reduce the surface temperature, an air-emitting perforation 3 is provided to form an air film 2 on the surface of the blade 1. Formation of perforations of desired diameter is required also in various other ceramic products such as water jet nozzles fuel injection nozzles, standard test samples, thermocouple elements, pen points and the like.
Ceramic materials having perforations have hitherto been produced by, for example, as shown in FIG. 3, subjecting a ceramic powder to mold pressing, subjecting the resulting shaped material to cold isostatic pressing, subjecting the resulting shaped material to binder calcination, conducting dry processing to form perforations and finally conducting firing, or conducting processing to form perforations after firing. In this case, perforation formation is conducted by the use of a drill, an ultrasonic wave, a laser beam or the like.
In the perforation formation using a drill, an ultrasonic wave, a laser beam or the like, however, it has been impossible to obtain very small perforations of 0.5 mm or less in inside diameter. Further, the depth (length) of perforation has been limited to at best 10 times the inside diameter. Furthermore, in the perforation formation using a laser beam, there has been a problem that the formed perforations have a tapered shape. There has also been a problem that no curved perforation can be obtained.
The present inventor made study in order to solve the above-mentioned problems of the prior art and, as a result, found that very small perforations of less than 0.5 mm in diameter can be formed in a ceramic material without employing machining. The present invention has been completed based on this finding.